A 3rd generation partnership project long term evolution (3GPP LTE) communication system will be described below as an exemplary mobile communication system to which the present invention is applicable.
FIG. 1 is a diagram schematically showing a network structure of an evolved universal mobile telecommunications system (E-UMTS) as an exemplary radio communication system. The E-UMTS system has evolved from the conventional UMTS system and basic standardization thereof is currently underway in the 3GPP. The E-UMTS may be generally referred to as a long term evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, refer to Release 7 and Release 8 of “3rd generation partnership project; technical specification group radio access network”.
Referring to FIG. 1, the E-UMTS includes a user equipment (UE), eNBs (or eNode Bs or base stations), and an access gateway (AG) which is located at an end of a network (E-UTRAN) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One or more cells may exist per eNB. A cell is set to use one of bandwidths of 1.25, 2.5, 5, 10, 15, and 20 MHz to provide a downlink or uplink transport service to several UEs. Different cells may be set to provide different bandwidths. The eNB controls data transmission and reception for a plurality of UEs. The eNB transmits downlink scheduling information with respect to downlink data to notify a corresponding UE of a time/frequency domain in which data is to be transmitted, coding, data size, and hybrid automatic repeat and request (HARQ)-related information. In addition, the eNB transmits uplink scheduling information with respect to UL data to a corresponding UE to inform the UE of an available time/frequency domain, coding, data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include the AG, a network node for user registration of the UE, and the like. The AG manages mobility of a UE on a tracking area (TA) basis, wherein one TA includes a plurality of cells.
Although radio communication technology has been developed up to LTE based on wideband code division multiple access (WCDMA), the demands and expectations of users and providers continue to increase. In addition, since other radio access technologies continue to be developed, new technology is required to secure competitiveness in the future. For example, decrease of cost per bit, increase of service availability, flexible use of a frequency band, simple structure, open interface, and suitable power consumption by a UE are required.
Multiple Input Multiple Output (MIMO) technology will hereinafter be described in detail. In brief, MIMO is an abbreviation for Multiple Input Multiple Output. MIMO technology uses multiple transmit (Tx) antennas and multiple receive (Rx) antennas to improve the efficiency of transmit/receive (Tx/Rx) of data, whereas the conventional art generally uses a single transmit (Tx) antenna and a single receive (Rx) antenna. In other words, MIMO technology allows a transmitter and a receiver to use multiple antennas so as to increase capacity or improve performance. If necessary, the MIMO technology may also be called multi-antenna technology.
In order to support MIMO transmission, the precoding matrix for properly distributing transmit (Tx) information to respective antennas according to a channel state or the like may be used.